Men who are habitual heavy drinkers, downing more than two pints of beer every day, are likely to start having the sort of memory lapses, that are commonly associated with ageing, up to six years early, according to a new study.

The long-term effect of alcohol on the brain has not been extensively researched. Most studies have looked at elderly people, who have usually stopped or considerably reduced their drinking.

The paper by scientists at University College London published in the journal Neurology looks at the drinking habits of a large group of middle-aged men and women and their performance in cognitive functioning tests – how well they think and remember things – 10 years later.

It appears to show that heavy drinking, at least in men, leads to significant deterioration over the long term.

Not enough women in the study were heavy drinkers for the scientists to conclude the same things happened to them.

The researchers, led by Séverine Sabia of the department of epidemiology and public health, analysed data that has been generated by the Whitehall II study, a massive group of civil servants whose health has been investigated over many years.

They focused on more than 5,000 men and 2,000 women who were aged 45 to 69 at the beginning of the study.

Their drinking habits were assessed three times over a decade. They took memory and executive function tests on three occasions. Executive functioning includes reasoning, task flexibility and problem-solving ability.

Heavy drinking men – defined in the study as those who drank more than 36g of alcohol a day, which is about four and a half units – began to suffer memory failures and deterioration in their cognitive processes between 18 months and six years earlier than those who drank less.

Light and moderate drinkers did not show declines.

Simon Ridley, head of research at the dementia research charity Alzheimer's Research UK, said: "These latest results could serve as one more reason to stick to any new year's resolutions to cut back on alcohol. Observational studies such as this can be important for identifying factors that may influence the risk of memory decline or disease, but it's difficult to pinpoint cause and effect with this type of research.

"The people in this study did not have dementia but memory decline can be a precursor to dementia and understanding the risk factors for this decline could be important for preventing the condition.

"This large study has yielded useful results, although it's not clear how far the findings from this group of civil servants can be generalised to the wider population.

"It's crucial to continue investing in research if we are to understand how to keep our brains healthy as we age and prevent the diseases that cause dementia.

"In the meantime, the best evidence suggests that in addition to not drinking to excess we can lower the risk of dementia by eating a healthy, balanced diet, keeping an eye on our blood pressure and weight, and taking regular exercise."